During the operation of industrial furnaces, for example in the steel industry, high temperatures occur in the waste gas, especially during a melting process, for example in an electric arc furnace. The high waste gas temperature is cooled down in a waste gas duct or flue by means of a water cooling circuit or by introducing additional water into the mass flow of waste gas before the waste gas is passed through a filter to the environment. The cooling down of the waste gas temperature is necessary for a downstream waste gas cleaning installation, since effective cleaning can only be achieved at a certain waste gas temperature. It is disadvantageous in this respect that electrical energy has to be used for operating the cooling circuit.
The heat extracted from the flow of waste gas by means of the cooling circuit in this case remains unused, since the flow of waste gas transported by the heat is too sporadic. On account of the way in which the installation is operated, both the volume flow and the temperature of the flow of waste gas are only constant in phases. The volume flow and/or the temperature may vary greatly in the different successive operating phases. There is consequently a discontinuous flow of waste gas with regard to the heat flow, the transported thermal energy of which cannot be readily used by conventional technical equipment, such as a heat exchanger for instance.